Conventional thin film read/write heads in data storage systems generally include an inductive write head in combination with either an inductive or magnetoresistive (MR) read head. Typically, an MR/inductive head includes an inductive write head formed adjacent to an MR read head.
During the manufacturing of thin film heads, rows of magnetic recording transducers are deposited simultaneously on wafer substrates using semiconductor type process methods. Thin film heads are generally multi-layer heads that require depositions and pattern construction, of alternating layers of magnetic films, insulators, and conductors on top of a substrate wafer (ceramic wafer). The substrate wafer is then cut into rows of sliders such that the pole tips of the inductive write transducers and the magnetoresistive stripes of the magnetoresistive read transducers, which are arranged in a side-by-side relationship, extend to an edge of the row. The surface of the row edge is then lapped to the optimum dimensions of throat height and stripe height. When separated from the slider rows, each slider contains a magnetic read/write head and an air-bearing surface configured to aerodynamically "fly" over the surface of a spinning magnetic disk medium.
One approach to lapping a slider row is to slice the substrate into rows of magnetic transducers, and, as described in the incorporated '877 patent, each row may be cemented to a lapping fixture for holding the slider row in position over a lapping plate. The lapping plate provides an abrasive surface for accurately lapping the row edge to a final dimension. Pressure actuators are used to push the lapping fixture into contact with the lapping plate such that the row edge of the substrate now may be lapped. The '877 patent provides electrical lapping guides at two opposite ends of the slider row. The lapping guides are monitored to provide position measurements of each end of the lapped edge. Thus, the level of the lapped edge may be determined and corrective forces applied to the slider row by the pressure actuators to maintain the lapped edge level with respect to the final throat height dimension of the transducer row.
As disk drive technology advances, the dimensions of the transducers are continually decreasing, and the tracks recorded on the disks are becoming narrower and closer together. Thus, a magnetic transducer must be manufactured with greater precision to maximize its efficiency and sensitivity to read and write data.
Typically, the combined inductive write transducer and magnetoresistive read transducer are formed from adjacent layers so as to read and write on the same track. The production of the transducers includes a sequence of deposition and etching steps with the magnetoresistive transducer formed first, and the inductive write transducer formed on top of the magnetoresistive transducer. The magnetoresistive transducer typically includes a magnetoresistive stripe, the height of which is critical, and is determined by the height defining edge, which is the bottom edge of the stripe. The inductive transducer typically includes a bottom pole and a top pole, separated by a gap. The inductive transducer poles are narrowed to a very narrow pole tip having a precisely controlled width, or throat, the width of which defines the recorded track width. The height of the throat is also an important factor in the optimization of the inductive transducer.
The throat height of the inductive transducer must be maintained within a limited tolerance for generating an optimum magnetic signal from the input electrical signal. Furthermore, the stripe height of the magnetoresistive read transducer must be maintained within a limited tolerance so that the optimum change in resistance is generated in response to the sensed magnetic signal. The magnitude of the critical dimensions of the pole tip and the stripe heights is in the order of a micron.
When placed in a lapping fixture, the accumulated stresses on the substrate row (or slider row), together with the extremely small dimensions of the transducers, may increase the chance that not all the transducers in the slider row will be precisely aligned with the lapping edge. This condition is defined in coassigned U.S. Pat. No. 4,914,868 as "row bow". The '868 patent addresses row bow by using the magnetoresistive transducers in the row of transducers as resistive elements and measuring the resistance of the resistive elements to determine the magnetoresistive transducer stripe height. A lapping fixture includes a holder which has a slider row temporarily cemented thereon for lapping. The fixture deflects the holder from a flat dimension to an appropriate shape to lap the row of transducers to the optimum magnetoresistive transducer stripe height for each of the transducers along the row, as measured by the magnetoresistive transducer resistances.
Another approach to lapping a slider row is to lap the row edge of a single slider row before it is sliced from the wafer or a section of the wafer. Cost savings of this approach results from the elimination of the row bond process, where the entire wafer is sliced into individual rows and each row is bonded to a single steel lapping tool beam for lapping. In contrast, each wafer in the low cost process is cut into multiple rectangular arrays of rows, each array called a "work piece". Typically, each row contains an equal number of magnetic transducers. Each wafer may be cut into six rectangular arrays of rows or work pieces, with four large primary work pieces and two small secondary work pieces.
Each work piece is bonded to an extender, and loaded into a lapping fixture. As the work piece is processed, a row is lapped to the desired stripe height, then the row is sliced off, and the next row is lapped.
The work piece and extender is a rigid body, unlike the flexible row substrate described above. Thus, if there is any residual stress from the fabrication of the wafer within the work piece, the transducers in the slider rows can be forced into a non-planar configuration, resulting in a wide distribution of stripe heights along the slider row. The rigid body typically does not undergo the row bending similar to the single slider row in the manner described in the '868 patent.
The wafer fabrication process may also create a radial stress pattern within the wafer. Radially, the stress within the wafer is tensile at the center region, converting to compressive at the perimeter region. Therefore, depending on the location of each work piece on the wafer substrate prior to being sliced into work pieces and its orientation, it may experience curvature due to tensile stress, compressive stress, or both types of stress, imparting different bow characteristics to each work piece.
Throughout the production process, the work piece shortens as slider rows are lapped and then sliced off. As a result, the residual stress within the work piece becomes more apparent with the diminishing stiffness of the work piece, thereby causing higher standard deviation of stripe heights for the lapped row. Unfortunately, the lapping system does not compensate for the increased bow of the work piece as the work piece shortens during lapping.